The April 18 announcement, a deal with Catalyst Health Solutions Inc., outstripped that deal and would create a combined company that covers 25 million members nationwide.

That would still be a fraction of the total pharmacy benefits marketplace, which is dominated by companies like CVS Caremark Crop. and the combined company formed by the merger of ExpressScripts Inc. and Medco health Solutions Inc.

With the acquisition of Catalyst, SXC could join the biggest players in the industry.

"You could start to say their name in the same breath," said Charles Rhyee, a New York-based equities analyst at Cowen & Co.

The merger mania is likely to prompt insurers and large employers to switch prescription benefit managers, which could open the doors for SXC down the road, if not right away.

"In our view, the companies saw an opportunity to generate value given the dislocation in the space — although the impact on this selling season remains a question," according to a note by analyst Amanda Murphy of New York-based investment firm William Blair & Co.

The combined company will remain based in Lisle, a western suburb of Chicago, and Thierer will continue as CEO and chairman of the combined company, the statement said.

The combined company expects $13 billion in revenue, rivaling the $13.9 billion in 2011 revenue reported by Deerfield, Illinois-based Baxter International Inc.

At that size, SXC would be the 15th-largest public company based in the Chicago area, according to Crain's 2011 list of the largest local public companies.

Shareholders of Rockville, Maryland-based Catalyst are to get $28 in cash and 0.66 shares of SXC stock for each Catalyst share, according to the statement. That equates to a price of $81.02 for each Catalyst share and a premium of about 28 percent based on the two companies' April 17 closing prices.

"This is an extremely compelling combination that brings together SXC's industry-leading tools and technology with Catalyst's full-service PBM, best-in-class service and growing client base to create a company that is even better positioned to compete in the marketplace," Thierer said in the statement.

The deal is expected to be completed in the second half of 2012. After closing, SXC shareholders are expected to own about 65 percent of the combined company, with Catalyst investors holding the remainder, according to the statement.